Many instruments, in particular balances, automatic titrators, automatic moisture analyzers and the like have to be set up in a horizontal position in order to function properly. In the case of balances, the horizontal position is necessary to prevent the weighing object on the balance from sliding off, to ensure that the weight force is directed perpendicular to the weighing 00pan, and to thereby achieve a more accurate weighing result.
In many cases, the instrument is equipped for this purpose with a plurality of adjustable feet, whereby the distance from the support surface to the underside of the instrument can be changed for the purpose of levelling the instrument.
In order to adjust this distance for example in accordance with U.S. Pat. No. 4,219,089 A or U.S. Pat. No. 6,407,351 B1, the adjustable foot has to be relieved of the weight of the instrument, which means that the instrument has to be lifted slightly off the support surface. This is so because the adjustable foot is configured as a screw that has to be turned into or out of the instrument against the increased resistance that is caused by friction if the foot is in contact with the standing surface. As a result, the levelling of the instrument becomes more difficult, as this procedure is inaccurate and hard to reproduce.
This problem is addressed for example in U.S. Pat. No. 5,332,182 A, which discloses an adjustment device that allows the height to be adjusted from outside the balance housing. By turning a knurled nut, a spindle is moved in the direction of the axis of rotation. A plate prevents the spindle from turning along with the knurled nut and in addition clamps the knurled nut between itself and the housing. The spindle is constrained against rotation by a flattened portion of its circumference and by a passage opening in the plate whose contour matches the cross-section of the spindle. A drawback of this arrangement is the amount of space needed, which is determined by the fully retracted spindle and its adjustable length.
The adjustment device of U.S. Pat. No. 5,332,182 A is easy to operate. The knurled nut protrudes over about a fourth of its circumference to the outside through a slot in the balance housing. Thus the height-adjustment device can be arranged in the interior of the balance housing while the adjustment can be performed from the outside. This is on the one hand a desirable trait, but on the other hand the adjustment device is not secured against inadvertent changes of the adjustment setting. However, in certain situations there may be a need to secure the adjustment device or to protect its setting against being inadvertently changed, as could happen for example in a quick manual cleaning around the balance with a dust rag.
A further disadvantage of the adjustment device of U.S. Pat. No. 5,332,182 A becomes evident when the device is examined with a view to sanitary standards. For example, open screw threads are not acceptable, as the threads may fill up with deposits which can breed germs. In addition, under a so-called “wash-down” standard, a surface radius of at least 3 mm is required. The “wash-down” standard applies to equipment which is suitable to withstand industrial cleaning by spraying with water and/or cleaning agents as well as mixtures thereof.
The objective of the present invention is to provide an adjustment device for a housing, specifically a balance housing, which overcomes the drawbacks of the prior art. Accordingly, the adjustment device should be of a configuration which can be realized within a limited height, which is easy to operate, and which is protected against inadvertent changes of the adjustment setting.